Display screen or portion thereof with a graphical user interface



The sole FIGURE is a front view of the display screen or portion thereof with a graphical user interface showing our new design.

The outermost broken line rectangle illustrates a display screen or portions thereof. The remaining broken lines illustrate portions of the graphical user interface. None of the broken lines form part of the claimed design.

The different shades of gray shown in the sole FIGURE represent a contrasting appearance of different portions of the graphical user interface. 

CLAIM We claim the ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 